Abrasive disc



. May 28, 1968 L H, VQRCE ET AL 3,385,010

ABRASIVE DISC Filed March 25, 1966 Il Y.

LELAND H'Fv:

oNEBk G. BELANGER ATTORNEY United States Patent Office 3,385,010 Patented May 28, 1968 3,385,010 ABRASIVE DISC Leland H. Vorce, Farmington, and Lionel G. Belanger, Southfield, Mich., assignors to Norton Company, Troy, N.Y., a corporation of Massachusetts Filed Mar. 25, 1966, Ser. No. 537,363 6 Claims. (Cl. 51-395) The present invention relates in general to coated abrasives and more specifically to coated abrasives in the configuration referred to in the art as an abrasive disc.

The normal abrasive disc is circular in form and is cut from a larger sheet r web of a coated abrasive material. The coated abrasive material is usually on either a cloth, fiber or paper backing suitably treated as is well known in the art. The abrasive grains, e.g. aluminum oxide, silicon carbide or various natural abrasive `materials are bonded to the backing by glue or resin adhesives or combinations thereof.

Variations from the normal circular configuration of abrasive discs have heretofore been proposed and a variety of these have found use in the art. Such shapes as hexagonal, octagonal and pentagonal are common-some with sharp intersecting points or corners and others with the intersections between the polygonal sides rounded to eliminate sharp junctures. A further non-circular periphery shape which has been found useful is the so-called rosette disc disclosed in U.S. 3,186,135.

However, all of these discs have possessed one disadvantage which has required that operators possess substantial skill. When grinding as on a metal surface such as a fender, unless extreme care is taken the discs of the prior art will all edge cut. That is, they will tend to bite deeper into the metal or other surface being sanded or ground at the point of contact between such surface and the peripheral edge of the disc. This will produce a variation in the surface which may be undetectable at the time of grinding but when the surface is finished it will show up as a wave or undulation of the surface -under the finish coat of paint, primer, varnish or the like. Particularly in production line operations as in the manufacture of automobile bodies, this tendency to edge cut causes serious problems of delays, reworking and expense.

Accordingly, it is an object of the present invention to provide a coated abrasive disc which overcomes this 4defect of prior art discs.

Another object of this invention is the provision of a coated abrasive disc which will not edge cut even when used by unskilled operators.

A further object of this invention is to provide a coated abrasive disc which has extreme fiexibility in its peripheral portions and which will not hook or engage with the workpiece being ground so as to cause damage to either the disc or the workpiece.

Additional objects, if not specifically set forth herein, will be readily apparent to one skilled in the art from the following detailed description of the invention.

In the drawings:

FIGURE 1 is a plan view of one embodiment of the coated abrasive disc of the present invention.

FIGURE 2 is a sectional view taken along the line 2 2 of FIGURE 1.

Generally, the present invention comprises forming a coated abrasive disc into a configuration having an interrupted non-circular periphery. The disc shape can be described as a circular central portion with a plurality of interrupted peripheral segments formed integrally with such central portion and uniformly spaced therearound. Each peripheral segment is separated from the next by a non-radial slot inclined from the periphery towards the interior of the disc in the direction in which the disc will be rotated in use. In the preferred construction, the boundary of the peripheral segment may be considered to be essentially defined by four boundary lines; the innermost being the arc of the circular central portion of the disc; the central outermost portion being formed by an arc having a radius less than the radius of the circular central portion but greater than 50% of such radius of such circular central portion; the trailing edge of such arc (i.e., the end of the segment which would Ibe the last to pass a given point when the disc is rotated in use) being connected to the innermost boundary line (the arc of the circular central portion) by a straight line substantially normal to the arc of said outermost central portion and hence at an angle to the continuation of any radius of the arc forming the central circular portion; and a last segment connecting the leading edge of the outermost central portion of the segment boundary with the innermost boundary and with the straight line section of the next adjacent segment. This latter boundary line may lbe arcuate or straight but either the straight line or a tangent to the arc if an arcuate boundary line is used will form an obtuse angle with the arc forming the central outermost portion. The exact point of contact between this line and the arc forming the outermost portion of the segment as well as the exact configuration of such line is not critical except that the point of contact which may be referred to as the leading edge of the segment should be further out from the circular central portion of the disc than the corresponding trailing edge of such segment. Variation in the location of the leading edge of the segment will cause variation in the area of the segment and hence it is generally maintained at only very slightly greater distance from the circular central portion than the trailing edge in order to maximize the cutting surface, i.e., the area of the peripheral segment.

More specifically and referring now to the drawings, FIGURES 1 and 2 show the preferred embodiment of the present invention. While the various boundary lines forming the peripheral segments may intersect at sharp points, it is preferred that each intersection be blended smoothly to avoid developing points of weakness which could result in failure of the disc in use and to help insure smooth cutting or grinding operations without snagging of the workpiece. Here reference numeral 10 refers to the coated abrasive disc with the abrasive surface 23 up or towards lone on .the drawing. This is important since the disc of this invention can rotate only in one direction in use. The direction of rotation is shown by the arrow on the drawing of FIGURE 1. The disc 10 may or may not have a central hole portion 1i1 for use in securing the disc to .the -back-up plate of a conventional grinder. Obviously, where it is desired to adhere the disc with adhesive, center hole 111 is not required. The disc 10 has a central circular portion `12 defined by the arc :13 shown in dotted lines. Extending outwardly from this central portion 12 are a plurality of spaced peripheral segments 14. These may be as few as five or six in number and as many as 16 to 20 as desired, so long as they are equi-spaced about the central circular portion 12. For most purposes eight segments have been found to be optimum as illustrated in FIGURE l.

lEach peripheral segment 14 is defined by the arc 113 of the central circular portion 12 of disc 10 having a radius R1; by an arc 115 having a radius R2; by a straight line section 16 and by a connecting line section 17 from the leading edge I18 of arc 15 t-o the arc 13. As indicated above, while these defining lines could meet at sharp points, it is preferred to utilize short arcs or curves to interconnect each to avoid weak spots and to enhance performance. As shown, the trailing edge 19 of peripheral segment 14 is connected through ya short arc 20 to straight line 16 while leading edge 1-8 is connected with an are 17 blended into arc 15 at the leading edge thereof. A short arc 21 then interconnects respectively arc L17 to the straight line section d6 of the next adjacent leading segment and straight line section 16 to arc 17 of the next adjacent trailing segment. Since each of these interconnecting arcs 2'1 are tangent to the arc of the central circular portion 112, they likewise interconnect the identified ends of each segment to said central portion. As previously pointed out, these peripheral segments 14 are actually integral with the central portion 12 of disc 10. Leading edge 18 is at a distance A from lthe arc 13 of the central circular portion 12 while trailing edge @19 is at a lesser distance B from the same arc 13. Although variations may be made within the general limits defined above, for illustrative purposes it may lbe pointed out that in the disc shown in FIGURES 1 and 2, the angle Y between the straight line section 16 and the extension of the radius R1 of the central circular portion 12 is 221/2 and the ratio of R1 to R2 is approximately 1:13, i.e., R2 is about 75% as long Ias R1. FIGURE 2 illustrates that in other respects the disc of the present invention is similar -to conventional coated abrasive discs, i.e., the disc 10 is formed of a backing member 22 which, as described above, may be paper, fiber, cloth or combinations thereof, and a uniform layer or layers of abrasive grain forming the abrasive surface 23 adhesively bonded to the upper surface of member 22. As clearly shown in FIGURE 2, the central portion 12 of disc 10 and peripheral segments l14 are integral and lie in substantially the same plane.

In operation, the disc ,10 is mounted, abrasive surface out, on the back-up plate of a conventional grinder and rotated in the direction of the arrow. The peripheral segments are, of course, not supported by the back-up pad, although usually and preferably such back-up pad will conform to and support the central circular portion \12 of the disc. The leading edge of each segment will first engage the work being abraded and will lead the segment per se smoothly into the work. The segment has exibility to conform yto the surface of the workpiece but is strengthened by the support derived from the straight line configuration at the trailing edge so as to effectively abrade. The lower relationship of the trailing edge to the leading edge of the segment in combination with the other Ifeatures of the disc have been found to make it virtually impossible to edge cut with the disc of this invention. A secondary advantage of the claimed configuration is the ability to view the area being ground by virtue of the interruptions between segments similar to the effect achieved by looking through the blades of an electric fan. Obviously, many modifications and variations may be made without departing from the spirit and scope of the invention described above and, therefore, only such limitations should be imposed as are contained in the appended claims.

We claim:

1. A coated abrasive disc comprising Ia continuous, substantially planar, abrasive coated base member having a circu-lar `central portion and a plurality of interrupted segments integral with said circular central portion, uniformly spaced therearound, and extending outwardly therefrom in the same plane as said central portion; each of said lsegments being separated from lthe next adjacent segment by a non-radial slot inclined from the pe-riphery towards the interior of the disc in the direction in which said disc is to be rotated in use; and each of said segments having its outermost periphery formed by an arc of lesser radius than the radius of said circular central portion; the leading edge, with reference to the direction in which said disc is rotated in use, of said outermost periphery of said segments being at a greater distance from said circular central portion than the trailing edge of said outermost periphery of said segments.

2. A disc as in claim 1 wherein the radius of the are forming the outermost periphery of each segment is at least fty percent of the lentgh of the radius 0f said circular central portion.

3. A disc as in claim 1 wherein at least a portion of the periphery of each such segment has a straight line edge.

4. A disc as in claim 3 wherein said straight line edge forms at least the leading edge, with respect to the direction in which said disc is rotated in use, of said nonriadial slot.

5. A disc as in claim 4 wherein said straight line edge is substantially normal to the are forming the outermost periphery of said segment.

6. A disc as in claim 4 wherein all intersecting edges of said segment, said circular central portion, and said non-radial slot are blended into each other with a smooth curve'.

References Cited UNITED STATES PATENTS 2,146,548 2/1939 Mitschang 51-378 3,139,709 7/1964 Walters 51-379 3,186,135 6/1965 Crean 51--394 FOREIGN PATENTS 1,318,689 41/1963 France.

ROBERT C. RIORDON, Primary Examiner. D. G. KELLY, Assistant Examiner. 

1. A COATED ABRASIVE DISC COMPRISING A CONTINUOUS, SUBSTANTIALLY PLANAR, ABRASIVE COATED BASE MEMBER HAVING A CIRCULAR CENTRAL PORTION AND A PLURALITY OF INTERRUPTED SEGMENTS INTEGRAL WITH SAID CIRCULAR CENTRAL PORTION, UNIFORMLY SPACED THEREAROUND, AND EXTENDING OUTWARDLY THEREFROM IN THE SAME PLANE AS SAID CENTRAL PORTION; EACH OF SAID SEGMENTS BEING SEPARATED FROM THE NEXT ADJACENT SEGMENT BY A NON-RADIAL SLOT INCLINED FROM THE PERIPHERY TOWARDS THE INTERIOR OF THE DISC IN THE DIRECTION IN WHICH SAID DISC IS TO BE ROTATED IN USE; AND EACH OF SAID SEGMENTS HAVING ITS OUTERMOST PERIPHERY FORMED BY AN ARC OF LESSER RADIUS THAN THE RADIUS OF SAID CIRCULAR CENTRAL PORTION; THE LEADING EDGE, WITH REFERENCE TO THE DIRECTION IN WHICH SAID DISC IS ROTATED IN USE, OF SAID OUTERMOST PERIPHERY OF SAID SEGMENTS BEING AT A GREATER DISTANCE FROM SAID CIRCULAR CENTRAL PORTION THAN THE TRAILING EDGE OF SAID OUTEROST PERIPHERY OF SAID SEGMENTS. 